Use a two-column proof to prove the Triangle Proportionality Theorem:

Step-by-step explanation:

From the picture attached,

                 Statements                                        Reasons

1). In ΔABC, DE intersects AB and AC  1). Given

2). DE║BC                                              2). Given

3). ∠ADE ≅ ABC                                    3). Corresponding angles postulate

4). ∠AED ≅ ∠ACB                                 4). Corresponding angles postulate

5). ΔADE ~ ΔABC                                  5). AA similarity postulate

6).                                           6). Definition of two similar triangles

Hence proved.  

the answer is b. 60. each interior angle in 120, so the exterior angle must be 60 in order to add up to 180

step-by-step explanation: